This invention relates generally to electromagnetic actuators and, in particular, electromagnetic actuators for driving blade mechanisms usable for exposure control purposes.
A wide variety of actuators have been used for driving shutter mechanisms in cameras. Typically, these tend to be mechanically sophisticated in construction and operation. Ordinarily, shutter blades are rotated, pivoted or generally linearly reciprocated for purposes of controlling the passage of scene light along an optical path which intersects the blades. U.S. Pat. Nos. 3,781,099; 3,782,255; and 3,942,183 are illustrative of different kinds of shutter blade arrangements. Many known kinds of shutter blade mechanisms include a stored energy device, in the form of a mechanically tensioned spring, for driving the blades to an open or closed condition. While they function satisfactorily and provide commercially acceptable reliability, nonetheless, they have certain limitations. As is apparent, sophisticated shutter mechanisms are of intricate construction and, therefore, are relative costly and difficult to manufacture. Moreover, with the use of spring mechanisms the performance characteristics are relatively fixed. This is disadvantageous since their performance characteristics cannot be programmable. Aside from this, the spring biased shutters have dynamic performance characteristics which are not as accurate or as reliable as they might otherwise be. Besides the foregoing drawbacks, they tend to be relatively large and somewhat bulky. Further, because of their complicated mechanical nature they are relatively susceptible to failure.
Recently, efforts have been undertaken for improving upon such shutter mechanisms. This is not only because of the limitations mentioned above, but also due to the desire to miniaturize cameras. In this connection, the use of relatively large spring tensioned devices for driving shutter blades in miniature cameras is less than entirely suitable.
Some proposals have suggested using electromagnetic actuators for driving the shutter blades. Many conventional electromagnetic actuators for actuating shutters employ annular field coils with magnetic armatures moving into and out of their cores. These are considered too bulky and, therefore, less than ideal for compact shutter mechanisms. U.S. Pat. No. 4,024,552 even discloses shutter blades which form part of the electromagnetic actuator itself for purposes of design simplicity. Despite this compact arrangement, such an actuator nevertheless uses springs for driving the blades to a terminal condition. In fact, a number of electromagnetic shutter mechanisms rely upon springs for driving the blades. Exemplary of such electromagnetic devices are those disclosed in U.S. Pat. Nos. 4,333,722; 4,338,009; and 4,348,092. Moreover, spring mechanisms tend to bias the shutter blades so as to make them dynamically unstable. Therefore, such systems typically employ latches to keep them in a stable at rest condition.
There have been proposals for springless shutter mechanisms. One such proposal is described in commonly-assigned U.S. Pat. No. 3,882,552. This patent discloses use of a rotary stepper motor for driving the shutter blades between open and closed orientations. Rotary stepper motors while being an improvement over the other kinds of conventional motors are still considered somewhat bulky for miniaturization purposes.
Another proposal for a springless type shutter mechanism is described in commonly-assigned U.S. Pat. No. 4,265,530 issued to the inventor of the instant application. This patent describes a system using not only a linear electromagnetic actuator but an electromagnetic clutching mechanism for intermittently transmitting the motive force of the actuator to the shutter blades.
A further proposal for a springless type shutter is disclosed generally in U.S. Pat. No. 4,121,235. This patent essentially discloses an electromagnetic shutter mechanism having a pair of solenoids each with an annular field coil which when actuated or energized actuate a pair of shutter blades interconnected through a force transmitting lever.